飞秒激光诱导图案独立显示研究

介绍了采用中心波长为800 nm的飞秒激光在不锈钢(316L)表面诱导产生独立显示图案的研究。结果表明,当扫描速率为15 mm/s,扫描行距为20 m,能量密度为1.1 J/cm2时,飞秒激光能够在不锈钢表面形成均匀的周期为540 nm的亚波长条纹结构。利用条纹结构的方向与激光光波偏振方向严格垂直的特性,通过改变激光偏振,可以在金属表面形成不同方向的条纹图案。在照明白光的辐照下,改变样品的方位角,形成的图案能够以彩色方式显示出来。此外,对使图案彩色显示的坐标区域与图案色彩能够覆盖的可见光谱范围进行了研究,并对其可能的应用进行分析。     

飞秒激光诱导图案独立显示研究

介绍了采用中心波长为800nm的飞秒激光在不锈钢(316L)表面诱导产生独立显示图案的研究。结果表明,当扫描速率为15mm/s,扫描行距为20μm,能量密度为1.1J/cm2时,飞秒激光能够在不锈钢表面形成均匀的周期为540nm的亚波长条纹结构。利用条纹结构的方向与激光光波偏振方向严格垂直的特性,通过改变激光偏振,可以在金属表面形成不同方向的条纹图案。在照明白光的辐照下,改变样品的方位角,形成的图案能够以彩色方式显示出来。此外,对使图案彩色显示的坐标区域与图案色彩能够覆盖的可见光谱范围进行了研究,并对其可能的应用进行分析。     

Evolution of the correlation between orthogonal polarization patterns in broad-area lasers

We measure polarization-resolved instantaneous patterns in a large-aspect ratio quasi-isotropic Nd:YAG laser. High correlation between the instantaneous orthogonal polarization patterns recorded at the earlier stages of the laser pulse has been found due to the strong cross saturation between both polarization modes.     

Spontaneous transverse patterns in a microchip laser with a frequency-degenerate resonator

We experimentally observe the formation of high-order transverse patterns in a microchip laser with a high degree of frequency degeneracy. With a doughnut pump profile the spontaneous transverse patterns are well localized in the Lissajous trajectories. The observed transverse patterns are reconstructed with a high degree of accuracy by use of the coherent state of quantum theory. The accurate reconstruction suggests that laser resonators can be designed to obtain a more thorough understanding of the quantum-classical connection.     

Fabrication and adhesion performance of gold conductive patterns on silicon substrate by laser sintering

Laser sintering of gold-microparticle ink was examined in this study. Laser-sintered gold conductive patterns were characterized by using scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), cross-cut tape test and destructive bond wire pull tests. The effects of laser power on microstructure and adhesion of gold conductive patterns were investigated. It was found that the microstructure of gold conductive patterns became denser with increase of laser power. The gold conductive patterns treated with laser power of 2 W showed poor adhesiveness of 2B in accordance with ASTM D3359-08. The adhesion level of gold conductive patterns increased to 5B by elevating laser power to 8 W. The adhesion mechanism of gold conductive patterns on silicon substrate was discussed and wire bonding test was also performed on gold conductive patterns. Wire breakage took place at the practical pull strength of around 5 gf.     

Robust technique of analyzing and locating laser speckle patterns for optical computer mice

Laser speckles have been used in measurement techniques, since they were discovered to be correlated with the displacement of the light source. This paper presents a robust technique of analyzing and locating laser speckle patterns (LSPs) for a prototype of a laser optical mouse. After the speckle images are captured from the image-grabbing device, they are analyzed by the proposed image processing procedures and normalized cross-correlation (NCC) is adopted to develop position-locating rules for laser speckle patterns. To verify robustness of the proposed approach, nine different materials of mouse pad are used. Experimental results show that they have all achieved similar and promising performance. Therefore, the proposed technique can not only precisely calculate the moving directions and displacement information for laser speckles, the linearity for the prototype of laser mouse can also be verified.     

Simultaneous forward- and backward-hemisphere elastic-light-scattering patterns of respirable-size aerosols

Two-dimensional angular optical scattering (TAOS) patterns of aerosols are measured simultaneously from the forward hemisphere 15 degrees < theta < 90 degrees as well as the backward hemisphere 90 degrees < theta < 165 degrees (detecting 63% of the 4pi sr of scattered light) by using an ellipsoidal reflector and an intensified CCD detector. TAOS patterns were obtained from polystyrene-latex spheres (individuals and aggregates) and from single Bacillus subtilis spores. These information-rich patterns, measured with a single laser pulse for individual particles on the fly, suggest that forward-TAOS and backward-TAOS measurements may be used for rapid classification of single aerosol particles.     

Formation and removal of multi-layered fluorescence patterns in gold-ion doped glass

We report the formation of fluorescence patterns inside gold-doped glass medium by femtosecond-laser fabrication. Strong fluorescence images appeared from the irradiated multi-layered region after low temperature annealing. We removed the images by exposing the glass to an electric furnace or a CO₂ laser beam for high temperature annealing. The method was also applied to recording, reading, and erasing of fluorescence data by a femtosecond laser, a 405-nm laser diode, and a CO₂ laser respectively.     

Constrained order in frustrated 2D optical patterns

In 2D optical patterns obtained in a Liquid Crystal Light Valve with optical feedback, we show a new kind of geometrical frustration which comes from the imposed form of the boundaries. The circular section of the incoming laser beam presents a symmetry which belongs to the O(2) group, whereas the optical feedback selects patterns with a symmetry restrained to a dihedral subgroup of O(2). By imposing boundaries which respect the symmetry of the dihedral group, we lift the frustration and obtain perfectly ordered patterns. Received 19 January 2001 and Received in final form 2 June 2001     

Wavelength dependence of intensity fluctuations in laser speckle patterns from biological specimens

Speckle patterns obtained when botanical specimens are illuminated with laser light are observed to fluctuate at a rate which depends on the wavelength of the light used. It is suggested that this wavelength dependence may be of value as an additional degree of freedom in some applications of intensity fluctuation spectroscopy.     

Spatial patterns induced in a laser beam by thermal nonlinearities

Stable spatial laser patterns were observed in a high-finesse Fabry-Perot cavity containing up to 2 atm of CO(2) and O(2). The gases displayed the same sequence of patterns that obey a scaling law of the form P(beta)p(2), where P is the power stored in the cavity, p is the pressure of the gas, and beta is a material-dependent parameter.     

采用六棱嵌镜分光器全视域显现衍射图样

1束激光在遮光门和2个同步旋转六棱嵌镜作用下分成3束,在几何衍射区、菲涅耳衍射区、夫琅禾费衍射区3个不同区域的不同位置形成参量不同的图样,这样既可利用视觉暂留现象进行同期观察,又可用感光片和数码相机拍摄或测量图样.     

Optical formation and manipulation of particle and cell patterns using a tapered optical fiber

A method for optical formation and controllable manipulation of particle and cell patterns using a tapered optical fiber is demonstrated. With a laser beam at 980‐nm wavelength launched into the fiber, different sized silica particles were formed into particle patterns (both one‐dimensional chains and two‐dimensional arrays) with different particle numbers by optical binding. The formed particle patterns can be controllably manipulated in three dimensions. Using yeast cells as an example, it was demonstrated that the method is applicable for the formation of biological cell patterns, without damage to the yeast cell viability. This method provides a new facile way for biophotonic and biological researches with particles and cells in a highly organized manner.     

Laser beam patterns of an optical cavity formed by two twisted cylindrical mirrors

Propagation of an elliptical Gaussian beam in a multiple-pass optical cell formed by two twisted cylindrical mirrors has been described by means of complex curvature tensors. Using the ABCD tensor approach various light patterns were computed for the use in tunable laser absorption spectroscopy with a multiple-pass optical cell. Light patterns with high beam-spot density can be also defined for a cavity formed by two twisted cylindrical high-reflectivity mirrors. In order to achieve higher cavity output intensity, a high-reflectivity cylindrical mirror cavity with at least one mirror that has a central transparent spot for laser beam injection has been described for applications in non-resonant cavity enhanced absorption spectroscopy. The author was with TDL Sensors Ltd., when the experimental part of this work was performed.     

Time-resolved dynamics of two-dimensional transverse patterns in broad area lasers

We report the first direct experimental observation of the fast dynamics (nanosecond scale) of complex two-dimensional transverse patterns in broad area lasers. The laser emission bright peaks forming the transverse patterns are observed to be aperiodically flashing in time with different growing rates. These optical filaments do not move along the cross section during their lifetime, which is close to 2 ns. The experimental observations have also been reproduced by numerical integration of the Maxwell-Bloch equations.     

Asymmetric stationary lasing patterns in 2D symmetric microcavities

Locking of two resonance modes of different symmetry classes and different frequencies in 2D resonant microcavity lasers is investigated by using a nonlinear dynamical model. The patterns of stationary lasing states and far fields are asymmetric in spite of the symmetric shape of the resonant microcavity. The corresponding phenomenon is actually observed in the experiment of a 2D semiconductor microcavity laser diode.     

Hyperbolic transverse patterns in nonlinear optical resonators

We consider a nonlinear optical system in general, and a broad aperture laser, in particular, in a resonator where the diffraction coefficients are of opposite signs along two transverse directions. The system is described by the hyperbolic Maxwell-Bloch equations, where the spatial coupling is provided by the D'Alambert operator rather than by the Laplace operator. We show that this system supports hyperbolic transverse patterns residing on hyperbolas in far-field domain, and consisting of stretched vortices in near-field domain.     

The effect of double heterojunction waveguide parameters on the far field emission patterns of lasers

A model of double-heterostructure lasers is developed which gives the far-field pattern of the laser in terms of such waveguide parameters as the active region width and the dielectric constants of the layers forming the waveguide. For symmetrical waveguides an explicit expression is given. Experimental results are presented which show a close agreement between the theory and the measured far-field patterns. By adding an extra passive layer to the conventional double heterostructure laser a structure is produced in which the measured half-power width of the far-field distribution is reduced from 55° to 32°. It is shown in this case that the model is useful for estimating the near-field pattern from the measured far-field pattern and hence determining the unknown waveguide parameters.     

Observation of the wave function of a quantum billiard from the transverse patterns of vertical cavity surface emitting lasers

We demonstrate experimentally that the near-field and far-field transverse patterns of a large aperture vertical cavity surface emitting laser (VCSEL) can be successfully interpreted as a two-dimensional (2D) billiard system. It is found that the near-field and far-field transverse patterns of a large aperture VCSEL evidently represent the coordinate-space and momentum-space wave functions of a 2D quantum billiard, respectively. The result of this paper suggests that large aperture VCSELs are potentially appropriate physical systems for the wave-function study in quantum problems.     

Influence of injection patterns on chaos synchronization performance between a multimode laser diode and a single-mode laser

In this paper, based on a system composed of a multimode emitted laser diode and a single-mode received laser, chaos synchronization performance has been investigated numerically under different optical injection patterns. The results show that, for single mode injection (SMI) which means the received laser is injected by a selective longitudinal mode of the multimode emitted laser whose wavelength corresponds to that of the single-mode received laser, the system synchronization performance is better than that with multi mode injection (MMI); depending on the optical spectrum of the received laser, the physical mechanism of chaos synchronization deterioration for MMI is given. Additionally, after taking into account the parameter mismatches, the chaos synchronization performance of the system with different injection pattern have also been discussed. For either SMI or MMI, the synchronization performance with negative parameter mismatches is better than that with positive parameter mismatches.